Biological nitrogen fixation contributes about 65% of the world's annual nitrogen fixation, and industrially produced nitrogen fertilizers, primarily produced by the Haber-Bosch process, accounts for 25% of the total annual nitrogen fixation. The Haber-Bosch ammonia process is presently the only available non-biological technology that has been commercially exploited. The Haber-Bosch process has a relatively high operational cost, operates at relatively high temperatures and pressures, and depends on non-renewable and depleting sources of energy.
Titanium dioxide (TiO2), or titania, is common soil constituent and a semiconducting material that can be photochemically stimulated by light energy. It is primarily extracted from sand deposits. Two active forms of TiO2 are commonly known in heterogeneous photocatalytic reactions, rutile and anatase, with anatase generally being photocatalytically more active.
In 1977, Schrauzer and Guth reported a successful photocatalytic synthesis of ammonia from atmospheric nitrogen by illuminating iron-doped TiO2 with ultraviolet (UV) light in the presence of water vapor. Since then, various attempts have been made to artificially fix elemental nitrogen using a variety of catalysts. Although some photocatalytic reactions fix nitrogen to a degree, none have been applied on an industrial scale, typically due to their low quantum yields.